VARIATIONS IN THE INFORMAL SOCIAL SYSTEMS OF 20 HIGH SCHOOLS, THE SOURCES OF THESE VARIATIONS, AND THE EFFECTS OF SUCH VARIATIONS ON THE ACADEMIC ATTITUDES AND BEHAVIOR OF STUDENTS WERE STUDIED. TWO RELATED ASPECTS OF THE SCHOOL SOCIAL ORGANIZATIONS RECEIVED MAJOR RESEARCH EMPHASIS--(1) THE CHARACTERISTIC GLOBAL DEMANDS, FEATURES, AND EMPHASES OF THE SCHOOL IN TERMS OF RELATIONSHIPS AMONG STUDENTS AND BETWEEN STUDENTS AND STAFF, AND (2) THE EXTENT TO WHICH ADOLESCENT PEER GROUPS EITHER REWARD ACADEMIC EXCELLENCE OR VALUE SOCIAL AND ANTISCHOOL ACTIVITIES. THE SAMPLE CONSISTED OF 20,345 STUDENTS, 1,029 TEACHERS, AND 20 PRINCIPALS. ALL THREE GROUPS COMPLETED SELF-ADMINISTERED QUESTIONNAIRES. IN ADDITION, STUDENTS WERE GIVEN TWO TESTS FROM PROJECT TALENT (FLANAGAN AND OTHERS, 1964) TO MEASURE APTITUDE FOR ABSTRACT REASONING AND ACHIEVEMENT IN MATHEMATICS. OTHER DATA WERE GATHERED FROM PERMANENT STUDENT RECORDS, INCLUDING IQ, GRADE POINT AVERAGE IN ENGLISH, AND ABSENTEEISM. OBTAINED FROM THE DATA GATHERING EXERCISE WERE MEASURES FOR THREE OTHER CLASSES OF VARIABLES--(1) VARIOUS DIMENSIONS OF SCHOOL CLIMATE AND ENVIRONMENT, (2) THE PERSONAL, ACADEMIC BEHAVIORAL, STUDENT ATTRIBUTES OF COLLEGE PREPARATION, PERSONAL VALUES ON INTELLECTUALISM AND ACHIEVEMENT, AND ACADEMIC ACHIEVEMENT IN MATHEMATICS AND ENGLISH, AND (3) SUCH PERSONAL AND BACKGROUND CHARACTERISTICS OF STUDENTS AS SEX, MENTAL APTITUDE, YEAR IN SCHOOL, AND SOCIOECONOMIC STATUS. THE LATTER CLASS OF VARIABLES WAS VIEWED AS A CLASS OF MEDIATING LINKS BETWEEN THE SCHOOL ENVIRONMENT AND THE INDIVIDUAL'S ACADEMIC BEHAVIOR. A SPECIAL STATISTICAL PROCEDURE WAS USED TO ESTABLISH A NUMBER OF RELATIONSHIPS AMONG THE CLASSES OF VARIABLES. A CONCOMITANT SEARCH WAS UNDERTAKEN TO IDENTIFY POTENTIAL SOURCES OF SCHOOL CLIMATE VARIATIONS, AND FINDINGS OF THIS EFFORT WERE (FOR THE MOST PART) NEGATIVE, BUT STILL SIGNIFICANT. A SECONDARY FOCUS OF THE OVERALL RESEARCH WAS AN EXPLORATORY ANALYSIS OF ACADEMIC DIFFERENCES BETWEEN NEGRO AND WHITE STUDENTS IN PREDOMINATELY WHITE HIGH SCHOOLS. (JH)